The CTA shut off power to the trains in that area, called the fire department and passengers were likely moved off the train and urged to use multiple bus lines in that area as an alternative as authorities investigated, according to Steele.

The Chicago Fire Department called an EMS Plan I, which automatically sends at least five ambulances to the scene.

No fire was found and crews did not learn what caused the sound, said Steele. The train was never stalled, added Steele.

The incident caused about 20-minute delays, but as of 8:30 a.m., normal service was resumed, he said.

The ambulance plan was secured about 8:30 a.m. and no one was taken to hospitals, according to the fire department.

The University of Illinois' rescinded job offer to a professor and a controversy over a faculty blog at Chicago State University helped land the two schools on a 2014 "worst of" list for student and faculty free speech rights.

Rep. Aaron Schock billed taxpayers at least three times for a total of more than $14,000 in private air travel last fall, including for a trip to a Chicago Bears football game, The Associated Press has learned.